Toward Scalable Fabrication of Atomic Wires in Silicon by Nanopatterning Self-Assembled Molecular Monolayers

Abstract

Developing a scalable method to fabricate atomic wires is an important step for building solid-state semiconductor quantum computers. In this work, we developed a selective doping strategy by patterning the selfassembled monolayer to a few nanometers using standard nanofabrication processes, which significantly improves the lateral doping resolution of monolayer doping from microscale to nanoscale. Using this method, we further explore the possibility to fabricate phosphorus wires in silicon by patterning self-assembled diethyl vinylphosphonate monolayers into lines with a width ranging from 500 to 10 nm. The phosphorus dopants are driven into silicon by rapid thermal annealing, forming dopant wires. Four-probe and Hall effect measurements are employed to characterize the dopant wires. The results show that the conductance is linear with the width for the wires, showing the success of the monolayer patterning process to nanoscale. To fabricate atomic wires made of one or a few lines of phosphorus atoms, we need to significantly shorten the thermal diffusion length and increase the dopant incorporation rate at the same time. Pulsed laser annealing may be a promising solution. The present work provides a promising pathway for mass fabrication of atomic wires in silicon that may find important applications in quantum computing.

Advances in ultrashallow doping of silicon

“…The diversity of organic molecules and the flexibility of self-assembly process make MLD an attractive and controllable doping technique. Dopants including phosphorus [20][21][22][23][24][25][26][27][28][29][30], boron [8,20,[31][32][33][34], nitrogen [35], arsenic [27,36] and antimony [37] have been introduced to silicon by MLD using commercial or synthetic reagents.…”

Towards Fabrication of Atomic Dopant Wires via Monolayer Doping Patterned by Resist-Free Lithography

“…This result can be interpreted by the diffusion induced attenuation in dopant concentration during thermal annealing process, as described in our previous report. [26] Using the mentioned method, we find the best fit when diffusion length √ 𝐷𝑡 ∼ 20 nm by enumerating possible diffusion lengths [green line in Fig. 3(c)].…”

“…( 2) following the "source-limited" diffusion model, where 𝑁 0 is surface dopant concentration, 𝐷 is diffusivity, 𝑡 is annealing time, and 𝑤 is line width. [26] 𝐶 (︁ 𝑥, 𝑦, 𝑡…”

“…Previously, we reported a selective doping strategy by nanopatterning self-assembled monolayers (SAM) to a few nanometers based on standard nanofabrication processes using hydrogen silsesquioxane (HSQ) resist. [26] While HSQ is widely used as negative resist for scientific research, it has poor resistance against hydrogen fluoride (HF) etching that was used to remove unprotected dopant-bearing molecules. As a result, it is challenging to use HSQ alone as an etching mask to nanopattern SAM layers.…”

“…Previously, we demonstrated that dopantbearing molecules can be removed with a combination of oxygen plasma and HF etching. [26] Considering that DVP molecules tend to be oxidized in the initial phase of PE-ALD process, the resultant phosphoruscontaining compounds can be readily removed by HF etching. XPS was used to characterize sample surfaces after the three sequential steps of surface modification and HF etching.…”